Audacity 2.2.2 Spectrogram and enabling spectral selection causes blotchy or smeared track

I commented procedure on the support file (.zip,) but the replicability has stopped once I started trying to document it.
At least I got a screenshot of the ‘blotchy’ effect I was describing. But not the ‘smear’ where most of the audio seemed to disappear too.

As it seems to have resolved itself now, I can get back to editing. I hope the logs are still useful to some interested devs.
Audacity_180919_spec_selec_blotchy.png (13 KB)

Was mainly using ‘Effect, Spectral edit shelves’.

Issue resolved after saved as new project name, not after closing and restarting Audacity. May be to do with specific file, or editing time?

(accidentally ?) turning down the spectrogram-range gives a similar look:
most of the display becomes an uninformative uniform-shade of gray …

same waveform, different spectrogram settings.jpg